The present invention relates to an image forming apparatus, such as a printer, a facsimile, etc., and specifically relates to a bottom structure of the mainframe in the image forming apparatus.
Image forming apparatuses in which a toner image is formed on a transfer sheet by developing a latent image formed on a photoreceptor drum (serving as an image forming member) with developer containing toner and transferring and fixing the developed toner image on the transfer sheet are well known. Such image forming apparatuses employ an electro-photographic image forming method and include electro-photographic copies, printers, facsimiles, etc., so to speak.
According with the market demands, there has been proposed various methods to improve the quality of images produced by the image forming apparatus mentioned above. Among them, the method of hardening the stiffness of bottom structure of image forming apparatus mainframe has been proposed. Namely, distortion of the image forming apparatus mainframe due to the low stiffness of its bottom structure deviates relative positions of various kinds of members, which are incorporated in the mainframe, from normal positional relationships, resulting in deterioration of positional accuracy between them. Specifically, in the electro-photographic image forming apparatus, the relative positions between the photoreceptor element, exposure means and developing means should be strictly maintained in a constant distance with high accuracy, otherwise serious problems for image quality, such as distortion of images, difference of image density, etc., would occur. Especially, in a color image forming apparatus, a serious problem such as a slide of a plurality of color images (for instance, color images of Y (Yellow), M (Magenta), C (Cyan)) would occur.
Although, conventionally, it has been well known that hardening the stiffness of-the mainframe is effective and important to maintain the quality of images formed by the image forming apparatus, there have been little knowledge what kind of bottom structure is actually effective to harden the stiffness of the whole mainframe.
For instance, in a general-purpose image forming apparatus, a box-type bottom structure, which is formed by bending peripheral edge portions of a single metal sheet, as shown in FIG. 6, is employed, namely, a pan-type shape in which one of two wide surfaces of a rectangular parallelepiped is excluded. The stiffness of such type of bottom structure, however, is not high so much, since the wide surface is liable to easily flex.
Further, it is known that, in a specific image forming apparatus, a quadrilateral frame-type structure, which is formed by joining two bended square pipe steels, as shown in FIG. 7, has been employed for the bottom structure. Although the stiffness of such type of bottom structure is higher than that shown in FIG. 6, it is not sufficient for recent image forming apparatus, which are increasingly expected to produce images with higher accurate image quality than ever.
For instance, recently, a certain image forming apparatus, having a total weight of 200 kg-300 kg, has been put into market. In such image forming apparatus, one part of support member of its bottom section should support around 50 kg-70 kg as an average weight, which is substantially equivalent to a human""s weight. Nonetheless, it is required such accuracy that the displacement, caused by the bending of bottom section, should be maintained within order of 100 xcexcm.
To overcome the abovementioned drawbacks in conventional image forming apparatus, it is an object of the present invention to provide an image forming apparatus, which makes it possible to maintain a higher accurate image quality by strengthening the stiffness of the mainframe.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by image forming apparatus described as follow.
(1) An image forming apparatus, which includes an image-bearing member and an image forming means for forming an image on the image-bearing member, comprising: a side section to substantially support at least one of the image-bearing member and the image forming means; and a bottom section to support and position the side section, wherein the bottom section comprises an upper surface member, a lower surface member and a side surface member which connects each side of the upper surface member and each side of the lower surface member.
(2) The image forming apparatus of item 1,
wherein the image-bearing member is a photoreceptor element for bearing a latent image, and the image forming means comprises a exposure device for exposing an image so as to form a latent image on the photoreceptor element and a developing device for developing the latent image with toner contained in developer.
(3) The image forming apparatus of item 2, wherein the side section substantially supports the photoreceptor element.
(4) The image forming apparatus of item 2, further comprising: a transferring device for transferring a toner image developed by the developing device onto a transfer sheet; and a fixing device for fixing the toner image on the transfer sheet.
(5) The image forming apparatus of item 1, wherein the image forming means forms color images on the photoreceptor element.
(6) The image forming apparatus of item 1, wherein the bottom section comprises a hollow space formed between the upper surface member and the lower surface member.
(7) The image forming apparatus of item 1, wherein the bottom section is shaped in a rectangular parallelepiped.
(8) The image forming apparatus of item 1, wherein the bottom section is formed by combining more than two pan-type members, each of which is formed by bending a peripheral edge portion of a single metal sheet, and thereby, the bottom section is substantially comprised of the side surface member, which connects each side of the upper surface member and each side of the lower surface member.
(9) The image forming apparatus of item 8, wherein the pan-type members are combined each other by means of a welding process.
(10) The image forming apparatus of item 8, wherein the pan-type members are combined each other by means of an adhering process with adhesive.
(11) The image forming apparatus of item 1, wherein the bottom section and the side section are combined each other by means of a welding process.
(12) The image forming apparatus of item 1, wherein the bottom section further comprises three supporting members located at a bottom surface of the lower surface member to support the image forming apparatus.
(13) The image forming apparatus of item 2, wherein both edge portions of the photoreceptor element are supported by two of the side sections, each of which comprises a plurality of side members to support one of the edge portions in an axial direction of the photoreceptor element.
(14) The image forming apparatus of item 2, wherein at least one of the exposure device and at least one of the developing device are also positioned at the side section.
(15) The image forming apparatus of item 1, wherein a pan-type lower member, in which the lower surface member and the side surface member are formed by bending a single metal sheet, is combined with the upper surface member to form the bottom section.
(16) The image forming apparatus of item 15, wherein a pan-type upper member, in which the upper surface member and the side surface member are formed by bending a single metal sheet, is combined with the pan-type lower member, in which the lower surface member and the side surface member are formed by bending a single metal sheet, to form the bottom section.
(17) The image forming apparatus of item 16, wherein the side surface member of the bottom section is formed by overlapping the side surface member of the pan-type upper member and the side surface member of the pan-type lower member each other.
(18) The image forming apparatus of item 16, wherein the pan-type upper member is combined with the pan-type lower member by putting one of them in another, to form the bottom section.
(19) The image forming apparatus of item 1, wherein all side surface of the bottom section is substantially closed by the side surface member.
(20) The image forming apparatus of item 2, wherein the exposure device includes a laser-beam generator.